Numerous designs have been advanced in an attempt to develop a cushioning device for footwear which is both protective and resilient, which yields and flexes to the degree necessary for comfort yet has sufficient stability and resistance to absorb impact and provide a supportive shield between foot and ground. The addition of an intermediate sole structure, filler, or padding has been employed in the past to minimize muscular and skeletal stress and attendant fatigue experienced in the feet and legs after standing or walking for long periods of time.
Early cushioning shoe sole designs are disclosed in U.S. Pat. Nos. 2,055,072 to Everston and 2,401,088 to Lumbard. The former employs thin plies of sponge rubber or the like layered between insole, midsole, and outer sole at heel, arch and ball areas. While the pads provide some cushioning, they are necessarily thin and only minor impact is required to compress them to a point at which they are no longer protective. The sole described in the latter patent employs two-ply fillers comprising a fibrous material cemented to a cushioning elastic material. Again, the materials and structure are such that this type of sole will withstand but a limited range of pressure or impact before full compression is reached. In more recent approaches to midsole construction, the development of layering techniques and the use of more resilient materials have resulted in soles which respond gradually and progressively to a greater range of compressive forces, thus providing more effective cushioning in a wider variety of situations. An example of this type of midsole structure is taught in my U.S. Pat. No. 3,834,046, granted Sept. 10, 1974. The shoe sole of my earlier invention comprises flexible upper and lower sheets formed with a plurality of complementary aligned ridges and channels, respectively. The ridges and channels are separated by an elastic diaphragm which yieldingly resists the compressive movement of the ridges into the open channels upon impact of the shoe against the ground. It is believed that the midsole structure of the present invention constitutes an improvement over the art of record, including that set forth in my earlier patent, as will be more clearly demonstrated hereinbelow.